Messages in this thread | | | Date | Sat, 18 Jul 2015 04:51:16 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH 13/21] x86/asm/crypto: Fix frame pointer usage in aesni-intel_asm.S |
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* Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Fri, Jul 17, 2015 at 12:44:42PM -0700, Andy Lutomirski wrote: > > On Fri, Jul 17, 2015 at 12:43 PM, Ingo Molnar <mingo@kernel.org> wrote: > > > > > > * Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > > > > >> ENTRY(aesni_set_key) > > >> + FRAME > > >> #ifndef __x86_64__ > > >> pushl KEYP > > >> movl 8(%esp), KEYP # ctx > > >> @@ -1905,6 +1907,7 @@ ENTRY(aesni_set_key) > > >> #ifndef __x86_64__ > > >> popl KEYP > > >> #endif > > >> + ENDFRAME > > >> ret > > >> ENDPROC(aesni_set_key) > > > > > > So cannot we make this a bit more compact and less fragile? > > > > > > Instead of: > > > > > > ENTRY(aesni_set_key) > > > FRAME > > > ... > > > ENDFRAME > > > ret > > > ENDPROC(aesni_set_key) > > > > > > > > > How about writing this as: > > > > > > FUNCTION_ENTRY(aesni_set_key) > > > ... > > > FUNCTION_RETURN(aesni_set_key) > > > > > > which does the same thing in a short, symmetric construct? > > > > > > One potential problem with this approach would be that what 'looks' like an entry > > > declaration, but it will now generate real code. > > > > > > OTOH if people find this intuitive enough then it's a lot harder to mess it up, > > > and I think 'RETURN' makes it clear enough that there's a real instruction > > > generated there. > > > > > > > How about FUNCTION_PROLOGUE and FUNCTION_EPILOGUE? > > Perhaps the macro name should describe what the epilogue does, since > frame pointers aren't required for _all_ functions, only those which > don't have call instructions. > > What do you think about ENTRY_FRAME and ENDPROC_FRAME_RETURN? The > ending macro is kind of long, but at least it a) matches the existing > ENTRY/ENDPROC convention for asm functions; b) gives a clue that frame > pointers are involved; and c) lets you know that the return is there.
So the thing I like about these:
FUNCTION_ENTRY(aesni_set_key) ... FUNCTION_RETURN(aesni_set_key)
is the symmetry - it's a lot harder to misplace/miswrite these than two completely separately named things:
ENTRY_FRAME(aesni_set_key) ... ENDPROC_FRAME_RETURN(aesni_set_key)
Also, the 'FRAME' part will be pointless and somewhat misleading once we do dwarves, right?
Another valid variants would be:
FUNCTION_ENTER(aesni_set_key) ... FUNCTION_RET(aesni_set_key)
or:
FUNCTION_START(aesni_set_key) ... FUNCTION_RET(aesni_set_key)
or:
ASM_FUNCTION_START(aesni_set_key) ... ASM_FUNCTION_RET(aesni_set_key)
Note that the name has two parts:
- The symmetric 'FUNCTION_' prefix tells us that this is a callable function that we are defining. That is a very significant property of this construct, and should be present in both the 'start' and the 'end' markers.
- The '_RET' stresses the fact that it always generates a 'ret' instruction.
Note what the names _don't_ contain: that we generate debug info! That fact is not present in the naming, and that's very much intentional, because the precise form of debug info is conditional:
- if CONFIG_FRAME_POINTERS=y then we push/pop a stack frame
- if (later on) we do CFI annotations we don't push/pop a stack frame but emit CFI debuginfo
In that sense 'FRAME' should never be in these names I think, nor 'PROC' (which is not symmetric).
Plus all 3 variants I suggested are very easy to remember, why I'd always have to look up any non-symmetric macro name called 'PROC'...
Thanks,
Ingo
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